TITLE:   GCN CIRCULAR
NUMBER:  33670
SUBJECT: GRB 230420A: Swift-BAT refined analysis
DATE:    23/04/21 14:58:39 GMT
FROM:    Tyler Parsotan  at NASA GSFC <tyler.parsotan@nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),  H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), M. Stamatikos (OSU) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 230420A (trigger #1164980) (Klingler, et al., GCN Circ. 33658). The BAT ground-calculated position is
RA, Dec = 161.040, 32.111 deg which is
   RA(J2000)  =  10h 44m 09.5s
   Dec(J2000) = +32d 06' 38.3"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).The partial coding was 100%.

The mask-weighted light curve shows possible pre-trigger activity with extended emission out to ~100 seconds. T90 (15-350 keV) is 111.75 +- 12.02 sec (estimated error including systematics).

The time-averaged spectrum from T-34.75 to T+100.80 sec is best fit by a power law with an exponential cutoff.  This fit gives a photon index 0.96 +- 0.46,  and Epeak of 70.6 +- 28.2 keV (chi squared 53.29 for 56 d.o.f.).  For this model the total fluence in the 15-150 keV band is 2.7 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+1.41 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index of 1.64 +- 0.10 (chi squared 60.99 for 57 d.o.f.).  All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1164980/BA/